Metal or plastic electrical junction boxes generally form a part of an electrical conduit or thermoplastic-sheathed cable (TPS) wiring system in a building. Electrical junction boxes can be designed for surface mounting and are used for mounting to ceilings, under floors or concealed behind access panels, particularly in residential or commercial buildings.
Some electrical junction boxes include built-in terminals for joining wires and form an integral part of a circuit protection system where circuit integrity has to be provided, for example, emergency lighting or emergency power lines.
Regardless of the type or function, electrical junction boxes provide connection points that allow residential or commercial wiring to be service and/or modified.